When Capt. Nilesh Gandhi’s oil tanker docked in coronavirus-ravaged China early last month, he understood that he would not be able to disembark and fly home as planned. He would have to keep working, at least until Singapore.

But when he arrived there, Singapore had prohibited all crew changes. And when he docks in Sri Lanka next week, the government there will ban him from getting off the ship. Saudi Arabia and the United Arab Emirates, his next two stops, forbid crew members from leaving, as well.

He is not alone. An estimated 150,000 crew members with expired work contracts have been forced into continued labor aboard commercial ships worldwide to meet the demands of governments that have closed their borders and yet still want fuel, food and supplies.

“We want to go home,” said Mr. Gandhi, 38, in a phone interview from aboard his ship.

His wife and son expected him home in Mumbai, India, more than a month ago. He said seven others — four Indians and three Filipinos — are similarly stranded on the ship. They are still being paid, but crew members say that, given the choice, they would have gladly declined the money and returned home.

Akin to wanting the mail but not the mailman, countries have insisted on keeping global shipping lines open while keeping seafarers out. Maritime organizations have lobbied governments to exempt crew members from travel bans, without success. Shipping companies say they are sympathetic, but need to keep commerce humming.

“That’s the most frustrating part,” Mr. Gandhi said. “They want the oil. They want no delays. They don’t want any disruptions. But when it comes to us, that’s where they have a problem.”

The result has been a string of desperate emails, text messages and calls to shore. Pleas to governments have gone unanswered. One human rights group said that it has been overwhelmed by emails and texts from seafarers who have been forced to stay onboard and work without their consent. A separate, much smaller group has been able to leave ships but cannot get home and is stranded ashore without salaries, saddled with hotel bills.

“This is not something we’ve come across before,” said David Hammond, the chief executive of Human Rights At Sea.

Some crew members have suggested an organized work stoppage that would bring the shipping lanes to a halt. But others say they would surely be blackballed in the industry if they refused orders to work.

“I have no choice but to keep working,” Gaurav Walia, a 31-year-old gas engineer, wrote in a text message from a tanker off the coast of Texas.

Seafaring contracts typically last between three and nine months, followed by unpaid time ashore. Crew members work long hours, seven days a week. Monthly salaries can range from as little as $400 for trainees to $1,000 for junior seamen and around $10,000 for captains. Under international maritime labor law, seafarers have a right to return home at the end of their contract at no cost to themselves.

“These are guys being made to do a prison term even though they haven’t been convicted,” said Frank Coles, chief executive officer of the Wallem Group, which provides crews for ships. “I know that sounds dramatic, but that’s essentially what’s going on.”

Mr. Coles has been outspoken in his calls for governments to do more to protect their workers.

The Philippines, China, India, Indonesia, Ukraine and Russia are among the biggest suppliers of crew members. Airline and port restrictions in most of these countries have made it nearly impossible for crew members to get home if the governments do not make special arrangements. Companies and crew members say China has allowed its own citizens to rotate at its ports.

Some regions are trying to solve the problem. On Monday, the European Commission allowed crew changes on continental ports and let seafarers return home. But even if a ship reaches an open port, crew members may still be out of luck because most international air traffic is grounded. Ports in Canada, for example, have remained open for crew changes, but flights home are often unavailable.

Mr. Coles said his company hurried an Indian crew member off a ship in the Netherlands recently, only to have him told that India would not accept any flights home. Mr. Coles said he had no choice but to put him back on the ship.

A representative of the Indian government in Brussels said that the country would work with seafarers trying to get home. But crew members say their appeals to Indian officials have gone unanswered. And an Indian government order, dated Monday, advised crew members to keep working indefinitely in all but the most extreme emergencies.

“They’ve been neglected and disregarded,” said Lakshmi Kannan, whose husband, Capt. Bejoy Kannan, was supposed to fly home to Kolkata, India, last week. Instead, the crew was held on board in South Africa and told to keep working. She and her daughters cried as he told them he could not say when he would return.

“For the first time in my life, I am worried,” Captain Kannan said. “I’ve never been worried facing a storm. I have never been worried about hectic operations or any natural calamities. But this time I’m worried.”

Maersk, one of the largest shipping lines in the world, has suspended crew changes on its container vessels for a month to maintain operations “as normal as possible.” The company said it was in the crew’s best interest.

“Given the current situation we can better protect our seafarers by suspending the exchange of crew, as this lessens the number of social interactions they need to have,” the company said in an email.

The International Transport Workers’ Federation, which represents seafarers, said it could not object to the mandatory extensions in the face of national laws closing borders.

“There was no alternative,” Fabrizio Barcellona, a federation official, said. “There is the legislation, you cannot go against it. We don’t want to put the seafarers at unnecessary risk themselves.”

Some contracts already include provisions for automatic one-month extensions. For many seamen, like Mr. Walia, those terms have expired and there is no end in sight. “I feel trapped and not doing well mentally,” he said in a text message.

Global trade will churn on, even at the expense of seafarers’ basic rights.

“We have to be pragmatic and decide what has to be done, and everybody has to accept that,” said Martin Dorsman, secretary general of the European Community Shipowners’ Associations. He noted that Dutch seafarers were away from home for six years during the Second World War.

“It’s very difficult to stick to rights,” he said.